This invention relates to magnetic storage apparatus capable of both high-density recording and high-speed transfer of data at a time, and particularly to one in which a high areal recording density can be achieved by suppressing the attenuation of the magnetic field intensity at high recording frequencies.
The induction-type thin-film magnetic head mounted on the conventional magnetic disk apparatus has its magnetic poles made of a NiFe alloy thin film of about 3 .mu.m in thickness. Since the resistivity of this NiFe alloy film is as low as around 16 .mu..OMEGA.-cm, the eddy-current loss is increased at high frequencies so that the recording magnetic field intensity is reduced. The amount of writing blur or overwrite value is changed with the recording frequency under the influence of this eddy-current loss. As a conventional example, there is, for example, JP-A-58-115612 in which it is described that the generation of eddy current affects the low-resistivity permalloy (such as NiFe alloy) in such a way as to reduce its high-frequency permeability, thus good reproduction characteristics (sensitivity) are not obtained. Because of these problems, the recording frequency at which the NiFe alloy thin-film head can operate is limited to about 30 MHz. On the other hand, the storage capacity of the magnetic disk apparatus has been steadily increased year after year, up to the extent that the now available 3.5-inch disk storage apparatus has an areal recording density of 350 Mb/in.sup.2, maximum. The data recording frequency at which this apparatus can record is around 27 MHz which is near the limit of the induction-type thin-film magnetic head using NiFe alloy thin films.